Thermostat frequently reboots or restarts on its own, especially when heating or cooling starts.

Safety first: Turn off power to the HVAC system before working on wiring.

• Step 1 – Tighten connections: At both thermostat and control board, tighten R and C terminals and ensure wires are fully inserted.
• Step 2 – Check cable length and gauge: If the thermostat is very far from the equipment and uses thin-gauge wire, consider upgrading to a thicker cable to reduce voltage drop.
• Step 3 – Measure voltage under load (advanced): With system running, measure AC voltage between R and C at the thermostat. If it drops significantly below 24 VAC when equipment starts, the transformer may be undersized or failing.
• Step 4 – Reduce accessory load: Temporarily disconnect non-essential accessories (humidifier, ERV) to see if reboots stop.
• Step 5 – Replace thermostat if needed: If supply voltage is stable but reboots continue, the thermostat may be defective.
• When to call a pro: A technician can evaluate transformer sizing and wiring to ensure reliable power.